1. Field of the Invention
Embodiments of the present invention generally relate to methods and apparatus for drilling with casing. More particularly, the present invention relates to methods and apparatus for coupling two strings of casings.
2. Description of the Related Art
In the oil and gas producing industry, the process of cementing casing into the wellbore of an oil or gas well generally comprises several steps. For example, a conductor pipe is positioned in the hole or wellbore and may be supported by the formation and/or cemented. Next, a section of a hole or wellbore is drilled with a drill bit which is slightly larger than the outside diameter of the casing which will be run into the well.
Thereafter, a string of casing is run into the wellbore to the required depth where the casing lands in and is supported by a well head in the conductor. Next, cement slurry is pumped into the casing to fill the annulus between the casing and the wellbore. The cement serves to secure the casing in position and prevent migration of fluids between formations through which the casing has passed. Once the cement hardens, a smaller drill bit is used to drill through the cement in the shoe joint and further into the formation.
Typically, when the casing string is suspended in a subsea wellhead or casing hanger, the length of the casing string is shorter than the drilled open hole section, allowing the casing hanger or high pressure wellhead housing to land into the wellhead prior to reaching the bottom of the open hole. Should the casing reach the bottom of the hole prior to landing the casing hanger or high pressure wellhead housing, the system would fail to seal and the casing would have to be retrieved or remedial action taken.
The difficulty in positioning the casing at the proper depth is magnified in operations where casing is used as the drill string. In general, drilling with casing allows the drilling and positioning of a casing string in a wellbore in a single trip. However, drilling with casing techniques may be unsuitable in the instance where the casing string must land in a wellhead. To reach proper depth to land a casing hanger or high pressure wellhead housing in the wellhead, the casing string must continue to drill to the proper depth. However, continued rotation while the casing hanger or high pressure wellhead housing is near, or in, the wellhead may damage the wellhead and/or it's sealing surfaces. Thus, the casing string may be prematurely stopped to avoid damaging the wellhead.
There is a need, therefore, for improved methods and apparatus for coupling two strings of casing. There is also a need for apparatus and methods for drilling with a casing and landing the casing in a wellhead.